Vision is sustained by a unique and beautiful relationship—that between photoreceptor cells and retinal pigment epithelial (RPE) cells. From the harmony of this cellular relationship emerges the life-long survival of the photoreceptor cell, despite the fact that the part of the eye where these cells interact is continuously exposed to potentially damaging factors. This relationship is one of the best examples of homeostasis in action as conceptualized for other cells and organs in 1932 by...